Extrachromosomal Elements in Lower Eukaryotes

Reed B. Wic1mer Section on Genetics of Simple Eukaryotes Laboratory of Biochemical Pharmacology National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases Bethesda, Maryland 20892 While most genes are chromosomal, the nonchromosomal genes have played a disproportionate role in molecular biology, in part because of their easy accessibility and in part because they represent the most mobile portion of a cell's genome. This is particularly evident in prokaryotes, where plas­ mids and phages have been the central objects of study. The lower eukaryotes, including fungi and yeasts, protozoa, slime molds, algae, and other single-celled nucleated species, have long had an important role in genetic research. They have recently gained dramatic popularity with the development of transformation methods for Saccharomy­ ~, Neurospora, Schizosaccharomyces, Dictyostelium, and others of this group. The realization that Saccharomyces has oncogenes, RNA tumor virus­ es, estrogens, a polypeptide sex hormone with close homology to human lactate dehydrogenase, intervening sequences, and all the mitotic, mito­ chondrial, and other structures typical of so-called "higher" eukaryotic organisms has confirmed the use of such organisms as model systems. Their use in biotechnology also shows great promise.

Organellar Genomes. - Mitochondrial Introns as Mobile Genetic Elements: The Role of Intron-Encoded Proteins. - Mobile Elements in the Yeast Mitochondrial Genome. - Mitochondrial Gene Expression in Yeast: Further Studies of a Self-Splicing Group II Intron. - The Mitochondrial DNA of Neurospora Crassa: Deletion by Intramolecular Recombination and the Expression of Mitochondrial Genes. - Initiation of Chloroplast DNA Replication in Chlamydomonas Reinhardtii. - Mitochondrial and Chloroplast Plasmids. - Mitochondrial Plasmids of Neurospora and other Filamentous Fungi. - The kalilo Senescence Factor of Neurospora Intermedia: A Mitochondrial IS-Element Derived from a Nuclear Plasmid. - Mitochondrial Plasmids in Cochliobolus Heterostrophus. - Linear Plasmids in the Phytopathogenic Fungus Claviceps Purpurea. - Mitochondrial Excision-Amplification Plasmids in Senescent and Long-Lived Cultures of Podospora Anserina. - Double-Stranded RNA Genomes. - Overview of Double-Stranded RNA Replication in Saccharomyces Cerevisiae. - Molecular Characterization of Chromosomal Genes Affecting Double-Stranded RNA Replication in Saccharomyces Cerevisiae. - The Replication of Double-Stranded RNA. - Structure and Function of the PET18 Locus of Saccharomyces Cerevisiae. - Sequence of the M1-2 Region of Killer Virus Double-Stranded RNA. - Analysis and Utilization of the Preprotoxin Gene Encoded in the M1 Double-Stranded RNA of Yeast. - Double-Stranded RNA and Hypovirulence of Endothia Parasitica. - Ustilago Maydis Virus-Encoded Killer System. - Symbionts. - Symbionts: An Overview. - Extrachromosomal Elements of Extrachromosomal Elements of Paramecium and Their Extrachromosomal Elements. - The Importance of the Refractile Body in Expression of the Killer Trait in Paramecium. - Structure and Characterization of Extrachromosomal DNA of Killer Xenosomes, Intracellular Symbionts of a Marine Protozoan. - Genetic Properties of Linkage Group XIX in Chlamydomonas Reinhardtii. - Omikron and Omikron-Like Endosymbionts of Euplotes. - Chlorella Algal Viruses. - Virus-Like Particles in a Soil Ameboflagellate, Naegleria Gruberi. - Bacterial Endosymbionts as Extrachromosomal Elements in Amebas. - Nuclear DNA Plasmids. - Survival Strategies of the Yeast Plasmid Two-Micron Circle. - Site-Specific Recombination Promoted In Vitro by the FLP Protein of the Yeast Two-Micron Plasmid. - Site-Specific Recombination of the Yeast Plasmid Two-Micron Circle: Intermediates in the Binding Process. - Two-Micron DNA-Like Plasmids from Non-Saccharomyces Yeasts. - Extrachromosomal DNA Elements in the Nucleus of Dictyostelium Discoideum. - Some Structural Aspects of Linear DNA Plasmids in Yeast. - Yeast DNA Replication. - Structural Studies on Centromeres in the Yeast Saccharomyces Cerevisiae. - Distribution of Telomere-Associated Sequences in Yeast. - Host Factors in Nuclear Plasmid Maintenance in Saccharomyces Cerevisiae. - Gene Expression. - Regulation of the Yeast CYC1 Gene. - Gene Cloning and Mutant Isolation for Subunits of RNA Polymerases in the Yeast Saccharomyces Cerevisiae. - Translation, Post-Translational Processing, and Mitochondrial Translocation of Yeast Iso-1-Cytochrome c. - Control of Yeast Gene Expression by Transposable Elements. - Roster of Organizing Committee, Chairmen, Speakers, and Participants.